The present invention relates to a multichannel wireless communication technology according to which a base station uses two or more channels to configure a cell including wireless communication terminals, and more particularly to a technology for controlling the use of channels between neighbor base stations.
Progress of an information society in recent years is very remarkable, and as a communication method for many information and communications apparatus and services, wireless communication is also used frequently other than wire communication.
Therefore, the demands for the radio frequencies whose use is limited are increasing continuously, and the depletion of frequencies that can be allocated is posing a big problem in every country in the world. In general, a country performs license management of the frequencies, and only those who are licensed to use can use the frequencies in the specific location and time period.
But, in order to satisfy the demands for frequencies which will increase continuously in the future, a new method of using the frequencies not being obsessed with the incumbent use method is being demanded.
Therefore, as a new method of using the frequencies to solve the depletion problem of the frequencies, studies are being made in these years to provide a method using a frequency band (for white space) which is not used spatially and timewise though it has already been allocated.
For example, research and development are being performed on a cognitive wireless communication system or the like by which an unlicensed user (hereinafter referred to as “secondary user”) uses the radio wave of the white space flexibly while the influence of the incumbent system for a licensed user (hereinafter referred to as “primary user”) to the frequency use is avoided sufficiently. See the Non Patent Literature 1: Koji Fujii, “Cognitive radio: Core technology of using white space to eliminate the waste of wave use”, RIC TELECOM, Retrieved on Jun. 9, 2011, on the Internet of businessnetwork.jp.
For example, in a wireless communication system using the white space, that is standardized by IEEE 802.22, respective radio stations access the database (DB) on an IP network by PAWS (Protocol to Access White Space database) to obtain a transmittable channel list (frequency list) based on the position information on a local station and maximum transmittable power. The transmittable channel list is collectively managed while it is being updated as required by a spectrum manager (SM) within a base station (BS). And, the BS determines a channel usable for communication as an operating channel according to the transmittable channel list and communicates with a wireless communication terminal (CPE: Customer Premises Equipment) such as a slave station, a cellular phone or the like, which is installed from door to door within a service area (cell) of the BS.
The SM manages spectrum sensing information. The respective radio stations (such as BS and CPE, the same applies below) are provided with a spectrum sensing function. Upon detecting by the spectrum sensing that the determined operating channel is being used by the incumbent system (system for the primary user), the respective radio stations notify the information to the SM. Then, the SM notifies the detected information to the DB and excludes the above channel from the transmittable channel list.
The wireless communication system using the white space performs dynamic spectrum access based on the information which is updated every moment as described above, avoids an influence to the frequency use by the primary user and also realizes communication of the secondary user.
Other functions provided to the SM include a function to share a list of operating channels (OPE) and a list of backup channels (BAK) with an adjacent BS, and according to such information, a channel can be selected exclusively not to cause interference between geographically closely positioned IEEE802.22 cells (adjacent cells). A Self Co-existence function (SC) is provided so that in a case where exclusive use is impossible, the channel is shared between the adjacent cells by time sharing. See the Non Patent Literature 2: “IEEE Std 802.22-2011 Part 22: Cognitive Wireless RAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications: Policies and Procedures for Operation in the TV Bands” edited by Institute of Electrical and Electronics Engineers (IEEE) Computer Society, (U.S.A.), IEEE Standards Association, Jul. 27, 2011.
FIG. 8 is a flow chart showing a flow to determine an operating channel after obtaining a list of channels usable by own cell and a channel list of all adjacent cells according to Non Patent Literatures.
Non Patent Literature 2 includes, for example, the following states as a state of channel.
AVA (Available): Channel notified as a usable white space by the DB.
OPE (Operation): Channel operating in the cell.
BAK (Backup): Operation candidate channel that is AVA and also judged as operable according to a sensing result.
LP1 (Local priority 1): Channel that is not OPE or BAK of an adjacent cell in the BAK.
LP2 (Local priority 2): Channel that is not OPE of an adjacent cell in the BAK.
LP3 (Local priority 3): OPE channel of an adjacent cell in the BAK.
Provided that an SCH (Superframe Control Header) or a CBP (Co-existence Beacon Protocol) is received from the adjacent cell, each BS can obtain a list of OPE and BAK channels of the adjacent cell. Then, a channel not causing interference between the adjacent cells is selected depending on the operating state of the channel of the adjacent cell.
The SCH is a frame header, which is transmitted at a top frame of the superframe having 16 frames as one control cycle, and includes an ID for uniquely identifying the BS and information on candidate channels for use.
The CBP is transmitted during a period called an SCW (Self Co-existence Window) allocated to the last of the uplink subframe, includes information on IDs and BAK channel numbers for uniquely identifying the BS similar to the SCH, and also includes information elements (IE), such as a frame release request (FC-REQ) for an ODFC (On-Demand Frame Contention) (FIG. 8, S104), a response (FC-RSP), a response acknowledgement (FC-ACK) and a release notification (FC-REL), which are used in a Self Co-existence mode.
First, the SM judges based on the operating channel information on the adjacent cell whether or not there is an exclusively available channel, namely a channel in a state of LP1 or LP2 (step S101).
And, when there are an exclusively available channel and LP1, a channel which is determined to be an OPE is selected out of the LP1, and when there is not LP1, a channel which is determined to be the OPE is selected out of the LP2 (step S102). In this case, a channel may also be selected according to the system specified standard, such as the order of priority of channel use, to determine its channel as an operating channel. For the order of priority, there is a way of following channel quality such as a CINR (Carrier power-to-Interference and Noise power Ratio), wireless communication regulation defined by the country, an operation rule for a network or a network operator's instruction.
On the other hand, when there is not an exclusively available channel, the SM judges whether or not the SC (Self Co-existence) mode can be performed (step S103).
When there is not LP3 or when the SC mode cannot be performed because of the wireless communication regulation defined by the country, the operation rule for a network or the network operator's instruction, the operating channel is not obtained, and BS operation is stopped, or waiting is made until an exclusively available channel becomes available.
When the SC mode can be performed, any channel is selected out of the LP3, and a channel operation right is obtained in a frame unit by randomized algorithm which is called as the ODFC from the OPE of the adjacent cell to realize channel sharing between cells by time sharing, or when interference can be avoided by synchronizing a downlink transmission/reception period (DS: Down Stream) and a uplink transmission/reception period (US: Up Stream) between cells, channel sharing is realized as a result.
The other prior art documents of the present invention is disclosed in Japanese Patent Application Publication No. 2009-515468.